[racket-dev] exact nonnegative integers as sequences?

On Mon, Apr 18, 2011 at 8:52 AM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> At Mon, 18 Apr 2011 08:34:34 -0500, Robby Findler wrote:
>> FWIW, I don't like that any of these 'in-*' thigns are optional. I was
>> recently reading over a script that was used to build web pages from
>> the output of testing runs for my compilers class and there were
>> several nested for loops without in-* thingies and it was painfully
>> difficult for me to reconstruct what the contracts of the functions
>> were because of that.
>
> Was the contract just "sequence", or did the values that were used as
> sequences in `for' also flow to places with more specific contracts?

These were not generic. The program didn't work unless the input was
an sexp with a particular structure (a table mapping names to outputs
and outputs and names were something specific too).

> (We probably agree that generic programming is good, so I'm trying to
> understand why it seemed counterproductive in your example.)


I agree about generic programming a general sense, but I'm not sure
about generic programming in this particular place: do you think that
there are many for loops out there there is no specific 'in-*' to put
in there? (And if there were, maybe it would be better to use a
keyword to say that explicitly?)

Matthias even says this implicitly in his message: I doubt he lets
lists be bound to "N" for example. So I don't think that this is about
generic programming.

I also don't buy Sam's implicit argument for my example. If I had
tried to port this to code to typed racket to just read off the types,
I would have spent far longer as debugging via TR's error messages is
going to be less productive than debugging via tracing the flow of
values in the program.

Robby